1. Field of the Invention
The present invention relates to an antiskid brake control system wherein when there is a tendency of a vehicle wheel to lock at the time of braking the vehicle, the action of an actuator causes a brake pressure to decrease, wherein when the revolution of the wheel has been restored due to such pressure reduction, the brake pressure is revived, and wherein these operations are repeated to prevent the wheel from coming into its lock state.
2. Discussion of Background
FIG. 5 is characteristic curves of a conventional antiskid brake control system as disclosed in e.g. Japanese Examined Patent Publication No. 20503/1984. In FIG. 5, reference numeral 101 designates vehicle wheel speed. Reference numeral 102 designates vehicle speed. Reference numeral 103 designates vehicle wheel deceleration in the vehicle wheel speed 101. Reference numeral 104 designates a brake pressure.
The operation of the conventional antiskid brake control system will be described. When the vehicle wheel deceleration 103 exceeds given value .alpha.1, the brake pressure 104 is decreased. When the vehicle wheel deceleration 103 is lowered to not higher than the given value .alpha.1 due to the decrease in the brake pressure, decreasing the brake pressure 104 is stopped, and the brake pressure 104 is slightly increased to compensate for a lag in operation of the brake system.
Next, when acceleration is produced at the wheel and the wheel acceleration has achieved not lower than given value .alpha.2, the brake pressure is held constant.
Next, when the wheel deceleration 103 lowers to not higher than the given value .alpha.2, the brake pressure 104 is increased.
The conventional antiskid brake control system works as forwards; when it detects a tendency of a vehicle wheel to lock at the time of braking, the brake pressure is decreased. When the vehicle wheel deceleration is lowered to not higher than the given first value, decreasing the brake pressure is stopped, and the brake pressure is increased until the vehicle acceleration exceeds the given second value. This allows a lag in operation of the brake system to be compensated. However, vehicle wheel deceleration characteristics greatly change depending on load conditions applied to the braked wheel, such as coefficient of friction between the road and the wheel, or on the gear position of a transmission.
Under such circumstances, the compensation for a lag in operation of the brake system becomes inadequate, and the antiskid brake control system gets into such state that the brake pressure is increased too much, or is decreased too much.
This creates problems in that the time required to obtain a proper value of braking force is prolonged, and the efficiency of the braking operation is significantly decreased, deteriorating a sense of brake operation.